The present invention relates generally to plugs, and more particularly relates to plugs for selectively plugging one of two different flow passages.
Although there may be other applications of the present invention, the present invention is particularly useful in oil pump applications for oil burner units. Oil burner units have in the past been provided with regulating valves interposed between the nozzles or nozzle which discharge fuel into the combustion chamber and the fuel pump which supplies fuel oil to the nozzles. Generally, these regulating valves open upon delivery of a predetermined supply pressure from the pump, regulate a substantially constant pressure flow to the burner nozzles, and shut off the supply of fuel oil to the nozzles when the pump is turned off upon shut down. In addition to regulating the pressure of fuel oil delivered to the burner nozzles, these valves have a bypass function of diverting an excess portion of the fuel oil pressurized and delivered by the pump back to the tank or pump reservoir so that only a portion of the fuel oil supplied by the pump is delivered to the nozzles. Oil pump units having a regulator valve for use with oil burner units are well known in the industry, and are generally disclosed in U.S. Pat. No. 5,692,680 to Harwath, U.S. Pat. No. 5,145,328 to Harwath, U.S. Pat. No. 3,566,901 to Swedberg, and pending U.S. patent application Ser. No. 10/017,153 to Mitchell, et al., the entire disclosures of which are hereby incorporated by reference.
Whether bypassed fuel is recirculated to the fuel tank or the local tank reservoir depends upon how the pump is set up. In either event, the oil pump units have two port openings, including a first port opening to allow for return to the local pump reservoir and a second port opening to allow for return to tank. In practice, the service technician or installing mechanic will typically plug one of the port openings to provide the desired flow path. To allow for selective installation, oil pump units are often sold with two different plugs, one to fit each different port opening. On occasion, service technicians or installing mechanics will make the mistake of installing both plugs at the same time which in turn can cause significant problems such as increasing upstream oil pressure and pump seal blowouts.
To overcome the problems existing in the art, the present invention is directed toward a plug for plugging a first port and blocking insertion of a second plug into a second port of a fluid system. The plug includes a threaded plug portion and a blocking stem portion extending from the threaded plug portion. The stem portion extends sufficiently from the threaded plug portion such that when the plug is mounted in the first port, the stem portion projects into the second port and blocks insertion or mounting of a second plug and thereby keeps the second port unplugged.
According to one aspect of the present invention, the plug is mounted into the return port of a oil pump unit for an oil burner to block return flow to the local reservoir of the pump (when bypassed flow is recirculated to the fuel storage tank). This prevents two plugs from being inadvertently mounted into the pump and blocking all return flow. The plug thus prevents excess upstream pressure build up and blown seals caused by improper installation of two plugs.